Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$36.86	9.559%	$40.3834	$40.38	$40.40	$40.40
Purchase #2	$143.34	8.182%	$155.0681	$155.07	$155.05	$155.10
Purchase #3	$113.81	12.369%	$127.8872	$127.89	$127.90	$127.90
Purchase #4	$205.27	8.353%	$222.4162	$222.42	$222.40	$222.40
Purchase #5	$124.37	6.575%	$132.5473	$132.55	$132.55	$132.50
Purchase #6	$238.66	7.608%	$256.8173	$256.82	$256.80	$256.80
Purchase #7	$207.91	5.609%	$219.5717	$219.57	$219.55	$219.60
7 purchase totals =	$1,070.22		$1,154.6912	$1,154.70	$1,154.65	$1,154.70